How many devices and tags one gateway can hold
A gateway receives its entire device configuration — every device on it, and every tag on those devices — as a single message. That message has a size limit set by the gateway's firmware, so the real limit is not a fixed number of devices or tags: it is how much configuration text they add up to.
That is why there is no "maximum 20 devices" setting anywhere. Ten devices with two tags each may fit comfortably while three devices with thirty tags each will not.
Roughly what fits
On current ESP32 firmware, a gateway holds in the region of 25 to 35 tags in total across all of its devices. Where you land in that range depends on how they are spread out: each device carries a little overhead of its own, so the same tag count costs more split across ten devices than concentrated on two.
As a rough guide, with alarm limits set on every tag:
| Devices on the gateway | Tags it will hold in total |
|---|---|
| 1–2 | about 35 |
| 3–5 | about 31–34 |
| 8–10 | about 24–27 |
Tags without alarm limits are cheaper, so you may fit somewhat more than this.
This is a large increase over earlier releases, where the same hardware managed about ten. The difference is not the hardware — it is that Synacl used to send the gateway a great deal of information it never read.
What happens when you reach it
You are told when you save. Adding the device or tag is refused, and the message names how many bytes you need to free.
Removing things is always allowed, including on a gateway that is already over the limit — so a gateway can always be brought back under it.
If you see this, you have three options:
- Remove tags you are not using. A tag you never chart or alarm on still costs space on the gateway. This is usually the quickest fix.
- Move some devices to a second gateway. Gateways are not capped by your plan, so splitting a large site across two units is a normal and supported thing to do.
- Update the gateway's firmware. Newer firmware can accept a larger configuration. See Updating gateway firmware (OTA).
If a gateway seems to be ignoring a new device
On releases before this limit was enforced, an oversized configuration was discarded by the gateway without any error — so a device could be added successfully and simply never produce readings, on a gateway that otherwise looked perfectly healthy.
If you are seeing that on an older release, updating Synacl resolves it. Afterwards, the gateway page shows whether the unit is running the current configuration, and you can use Resend config to push it again.
Applying a configuration restarts the gateway. This is normal and takes under a minute. It happens when the configuration actually changes — not on every save, and not on a resend when the gateway is already up to date.